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Precambrian |
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Time: |
4600 to 570
mya |
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Duration: |
4030 million years |
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Coal-like material has been identified in Precambrian rocks of the
Canadian Shield in Canada and the United States. These deposits are small, thin, and have
a high ash content. They are either noncombustible or have a very low heat value. Because
plants with woody tissue did not develop until the Devonian, these coals are not humic
coal. The deposits were probably formed from algae deposited on the margins of a sea
making them sapropelicitic. |
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